Rainfall Intensification Enhances Deep Percolation and Soil Water Content in Tilled and No-Till Cropping Systems of the US Midwest

Globally, the proportion of total rainfall occurring as extreme events is increasing, which may have consequences for agriculture. In the US Midwest, we conducted a 234-d manipulative experiment in 16 paired plots where we increased the proportion of rain falling in extreme events on tilled and no-till cropping systems. We compared the effects of larger, less frequent rain events (intensified rainfall) vs. smaller, more frequent rain events (normal rainfall) on soil water content and deep percolation. The effect of intensified rainfall on the volumetric water content (VWC) of soil at the 10-cm depth during the experiment varied seasonally: in spring, intensified rainfall decreased the average VWC at the 10-cm depth by 0.05 +/- 0.01 cm(3) cm(-3) compared with normal rainfall, but in summer and fall, it had no effect. In soil at the 100-cm depth, VWC declined during the summer in normal but not intensified plots. A surface-added Br- tracer was detected and peaked earlier in soil water at 120 cm under intensified rainfall vs. normal rainfall (by 6 +/- 3 and 74 +/- 33 d, respectively) regardless of tillage, although it was detected sooner in no-till than tilled systems (by 9 +/- 3 d). Also, less Br- was recovered in soil under intensified (8 +/- 8% of total Br- added) vs. normal rainfall (21 +/- 3%). Our results suggest that rainfall intensification will increase deep percolation and deep soil water content in cropping systems regardless of tillage. Such changes to soil water dynamics may alter plant water and nutrient availability.